The present invention relates to a process for producing a perfluorolactone. More particularly, it relates to a process for producing a perfluorolactone having the formula ##STR2## by reacting a fluoro compound having the formula EQU I(CF.sub.2).sub.n COX
with fuming sulfuric acid.
The perfluorolactones are remarkably useful as intermediates for various fluorine-containing compounds or compounds having special characteristics. For example, the perfluorolactones can be easily converted to the corresponding perfluorodicarboxylic acid derivatives by reacting with a nucleophilic reagent.
These derivatives can be effectively used as polybasic acids for producing fluorine-containing condensation polymers such as polyamides or polyesters.
On the other hand, the perfluorolactones are intermediates useful for synthesis of various fluorine-containing vinyl monomers especially fluorine-containing vinyl ethers, and they impart excellent characteristics such as lubricants, fiber processing agents, etc..
Thus, these useful perfluorolactones have been hard to produce in high yield. Moreover, complicated processes have been required for producing them.
A satisfactory industrial process for producing them has not been known. For example, perfluoro- .gamma.-butyrolactone has been produced by heating disilver perfluoroglutarate at 125.degree. C in the presence of iodine by R. E. Banks et al.
However, the yield of the object compound of perfluoro- .gamma.-butyrolactone was only 8% or less (JCS (C( 1967, 2333).
The inventors have found that perfluorolactones can be produced in high yield by reacting .alpha.,.omega.-diiodoperfluoroalkane having 3 to 5 of carbon atoms with fuming sulfuric acid.
However, when 1,4-diiodoperfluorobutane is used as starting material, the corresponding perfluorolactone can be obtained in about 50 to 60% of yield, and the reaction product usually contains 10 to 15% or more of perfluorodicarboxylic fluoride.
Since both compounds have similar boiling point, it is hard to obtain the perfluorolactone having high purity by separating them.